Metastructure having zero elastic modulus zone and method for designing metastructure having zero elastic modulus zone

ABSTRACT

Disclosed herein are a metastructure having a zero elastic modulus zone, which can experience constant stress in a predetermined strain zone, and a method for designing the same. The metastructure includes a first unit and a second unit, wherein the first unit has a structure capable of buckling and has a stress-strain relation having a zone corresponding to a negative elastic modulus, the second unit is disposed adjacent to the first unit and has a stress-strain relation having a zone corresponding to a positive elastic modulus, and the metastructure has zero elastic modulus in a predetermined target strain zone through synthesis of the negative elastic modulus of the first unit with the positive elastic modulus of the second unit.

TECHNICAL FIELD

The present invention relates to a metastructure having a zero elasticmodulus zone and a method for designing the same and, more particularly,to a metastructure having a zero elastic modulus zone, which canexperience constant stress in a predetermined strain zone, and a methodfor designing the same.

BACKGROUND ART

There are various applications requiring uniformity in loaddistribution. Examples of such applications include a mattress orcushion for preventing bedsores occurring in bedridden patients, atransfer film that can provide uniform contact pressure to devices in adevice transfer process, a control unit for passive load control orpassive pressure control, and the like.

In particular, taking a transfer film used in a device transfer processas an example, production equipment used in semiconductor processes,flexible electronics processes, display processes, MEMS processes, LEDprocesses, solar cell processes, and the like requires an apparatus fortransferring thin film-type devices. A thin-film device used in flexibleelectronic products is required to have a very small thickness to beflexibly bent. In general, it is known that a monocrystalline siliconthin-film device is required to have a thickness of 5 μm or less to bebent to a curvature of 0.5 mm diameter when assumed to have a fracturestrain of 1%.

For typical thick devices, a transfer process including picking andplacing is performed using vacuum chuck technology. However, whenapplied to thin devices, the vacuum chuck technology has a problem inthat the devices can be damaged due to pressure generated by a vacuumchuck. Accordingly, vacuum chuck technology is generally inapplicable tothin-film devices having a thickness of 5 μm or less.

In addition, there is a method of transferring devices using anelectrostatic chuck. However, when applied to thin devices, this methodhas a problem in that the devices can be damaged due to staticelectricity.

For the above reasons, technology of attaching or transferringultra-thin devices using van der Waals force acting on a nanoscale isknown in the related art. In particular, a transfer apparatus capable ofcontrolling van der Waals force is used to transfer thin-film devices.However, if the transfer apparatus has a very hard surface, good contactbetween the transfer apparatus and thin-film devices cannot beestablished due to a slight thickness difference between the devices, acurvature of a substrate, and the like, making it impossible to achieveadhesion of the devices to the transfer apparatus and transfer of thedevices by the transfer apparatus. Therefore, a transfer apparatusmanufactured using a material having a very low elastic modulus, forexample, a polymer or rubber, is used to transfer such thin-filmdevices. One example of such a transfer apparatus is a flexible stamp.

In general, transfer apparatuses may be classified into a roll type anda plate type.

In the roll-type transfer apparatus, a roller is disposed on asubstrate. Here, the roller is provided on an outer circumferentialsurface thereof with an adhesive layer to which micro-devices to betransferred to the substrate are adhesively attached.

In the plate-type transfer apparatus, a pressure plate is disposed on asubstrate. Here, the pressure plate is provided on a lower surfacethereof with an adhesive layer to which micro-devices to be transferredto the substrate are adhesively attached.

In the roll-type transfer apparatus or the plate-type transferapparatus, it is important to allow uniform contact pressure to beapplied between the adhesive layer and multiple micro-devices in orderto ensure that the multiple micro-devices are picked from a sourcesubstrate onto the adhesive layer or that the multiple micro-devicesadhesively attached to the adhesive layer are placed on a targetsubstrate.

However, it can be difficult to provide uniform contact pressure betweenthe adhesive layer and the micro-devices due to tolerances for thetransfer apparatus, such as machining errors of the roller or thepressure plate and assembly tolerances, uneven heights of themicro-devices, warpage of the substrate, and the like.

Then, a micro-device at a location where insufficient contact pressureis applied cannot be properly transferred, whereas a micro-device at alocation where excessive pressure is applied can be compressed anddamaged.

Therefore, there is a need for technology that can solve non-uniformityof contact pressure distribution due to various errors.

DISCLOSURE Technical Problem

Embodiments of the present invention are conceived to solve suchproblems in the art and it is an object of the present invention toprovide a metastructure having a zero elastic modulus zone, which canexperience constant stress in a predetermined strain zone, and a methodfor designing the same.

It will be understood that objects of the present invention are notlimited to the above. The above and other objects of the presentinvention will become apparent to those skilled in the art from thedetailed description of the following embodiments in conjunction withthe accompanying drawings

Technical Solution

In accordance with one aspect of the present invention, a metastructurehaving a zero elastic modulus zone includes: a first unit having astructure capable of buckling and having a stress-strain relation havinga zone corresponding to a negative elastic modulus; and a second unitdisposed adjacent to the first unit and having a stress-strain relationhaving a zone corresponding to a positive elastic modulus, themetastructure having zero elastic modulus in a predetermined targetstrain zone through synthesis of the negative elastic modulus of thefirst unit with the positive elastic modulus of the second unit.

In one embodiment, the first unit may include: a first upper frameextending horizontally; a first lower frame extending horizontally andspaced apart from the first upper frame; and a pair of first supportframes each connected at an upper end thereof to the first upper frameand connected at a lower end thereof to the first lower frame, adistance between the pair of first support frames increasing toward thefirst lower frame such that the pair of first support frames bucklesupon application of compressive load.

In one embodiment, the first unit may further include: a slit formedthrough the first support frame and extending in a longitudinaldirection of the first support frame.

In one embodiment, the second unit may include: a second upper frameconnected to the first upper frame and extending horizontally; a secondlower frame connected to the first lower frame and extendinghorizontally; and a pair of second support frames each connected at anupper end thereof to the second upper frame and connected at a lower endthereof to the second lower frame, a distance between the pair of secondsupport frames increasing toward centers thereof such that the pair ofsecond support frames is deformed without buckling upon application ofcompressive load.

In one embodiment, the first upper frame may be integrally formed withthe second upper frame, and the first lower frame may be integrallyformed with the second lower frame.

In one embodiment, the first unit and the second unit may be formed ofthe same material.

In one embodiment, the metastructure may include multiple metastructuresarranged on a virtual plane, and the first unit and the second unit maybe alternately arranged to be adjacent to each other.

In one embodiment, the first unit and the second unit may be stacked inmultiple layers.

In accordance with another aspect of the present invention, a method fordesigning a metastructure having a zero elastic modulus zone includes: afirst unit formation step in which a first unit is formed, the firstunit having a structure capable of buckling and having a stress-strainrelation having a zone corresponding to a negative elastic modulus; asecond unit formation step in which a second unit is formed, the secondunit being disposed adjacent to the first unit and having astress-strain relation having a zone corresponding to a positive elasticmodulus; and a compensation step in which the negative elastic modulusof the first unit is synthesized with the positive elastic modulus ofthe second unit such that the metastructure has zero elastic modulus ina predetermined target strain zone.

In one embodiment, in the compensation step, when an elastic modulusprofile obtained through synthesis of the negative elastic modulus ofthe first unit with the positive elastic modulus of the second unit hasa slope greater than zero in the target strain zone, an adjustment maybe made to increase an absolute value of the negative elastic modulus ofthe first unit or to reduce an absolute value of the positive elasticmodulus of the second unit.

In one embodiment, the first unit may include first upper and lowerframes each extending horizontally and vertically spaced apart from eachother and a first support frame connected at an upper end thereof to thefirst upper frame and connected at a lower end thereof to the firstlower frame, the first support frame buckling upon application ofcompressive load; the second unit may include a second upper frameconnected to the first upper frame and extending horizontally, a secondlower frame connected to the first lower frame and extendinghorizontally, and a second support frame connected at an upper endthereof to the second upper frame and connected at a lower end thereofto the second lower frame, the second support frame being deformedwithout buckling upon application of compressive load; and, in thecompensation step, when an elastic modulus profile obtained throughsynthesis of the negative elastic modulus of the first unit with thepositive elastic modulus of the second unit has a slope greater thanzero in the target strain zone, an adjustment may be made to reducelengths of the first upper frame and the first lower frame or toincrease lengths of the second upper frame and the second lower frame.

In one embodiment, the first unit may include first upper and lowerframes each extending horizontally and vertically spaced apart from eachother and a first support frame connected at an upper end thereof to thefirst upper frame and connected at a lower end thereof to the firstlower frame, the first support frame buckling upon application ofcompressive load; the second unit may include a second upper frameconnected to the first upper frame and extending horizontally, a secondlower frame connected to the first lower frame and extendinghorizontally, and a second support frame connected at an upper endthereof to the second upper frame and connected at a lower end thereofto the second lower frame, the second support frame being deformedwithout buckling upon application of compressive load; and, in thecompensation step, when an elastic modulus profile obtained throughsynthesis of the negative elastic modulus of the first unit with thepositive elastic modulus of the second unit has a slope greater thanzero in the target strain zone, an adjustment may be made to increasethicknesses of the first upper frame and the first lower frame or toreduce thicknesses of the second upper frame and the second lower frame.

Advantageous Effects

According to embodiments of the present invention, a metastructurehaving a zero elastic modulus zone includes a first unit having astress-strain relation having a zone corresponding to a negative elasticmodulus and a second unit having a stress-strain relation having a zonecorresponding to a positive elastic modulus. The metastructure can havezero elastic modulus in a predetermined target strain zone throughsynthesis of the negative elastic modulus of the first unit with thepositive elastic modulus of the second unit. Accordingly, themetastructure can provide uniform adhesion pressure to all devices to betransferred even when each of the devices applies a different amount ofpressure to the metastructure due to various factors.

It will be understood that advantageous effects of the present inventionare not limited to the above and include any advantageous effectsconceivable from the features disclosed in the detailed description ofthe present invention or the appended claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a metastructure having a zero elasticmodulus zone according to one embodiment of the present invention.

FIG. 2 is a front view of the metastructure of FIG. 1 .

FIG. 3 shows a view illustrating deformation of a first unit of FIG. 1and a graph of the resulting stress-strain relation.

FIG. 4 shows a view illustrating deformation of a second unit of FIG. 1and a graph of the resulting stress-strain relation.

FIG. 5 shows a view illustrating deformation of the metastructure havingthe zero elastic modulus zone of FIG. 1 and a graph of the resultingstress-strain relation.

FIG. 6 is an exemplary view illustrating the relationship between strainand adhesion pressure in a conventional stamp.

FIG. 7 is an exemplary view illustrating the relationship between strainand adhesion pressure in the metastructure having the zero elasticmodulus zone of FIG. 1 .

FIG. 8 is a diagram illustrating an example of parallel arrangement ofmetastructures each having a zero elastic modulus zone as shown in FIG.1 .

FIG. 9 is a flowchart of a method for designing a metastructure having azero elastic modulus zone according to one embodiment of the presentinvention.

FIG. 10 is an exemplary view illustrating an example of shape adjustmentof the first unit of FIG. 1 .

FIG. 11 is an exemplary view illustrating an example of shape adjustmentof the second unit of FIG. 1 .

FIG. 12 is a graph describing a compensation step of FIG. 9 .

FIG. 13 shows an exemplary view of a serial array of metastructures eachhaving a zero elastic modulus zone as shown in FIG. 1 and a graph of theresulting stress-strain relation.

LIST OF REFERENCE NUMERALS

100: Metastructure having zero elastic modulus zone

110: First unit

111: First upper frame

112: First lower frame

113: First support frame

114: Slit

130: Second unit

131: Second upper frame

132: Second lower frame

133: Second support frame

BEST MODE

Reference will now be made in detail to various embodiments, examples ofwhich are illustrated in the accompanying drawings. It should beunderstood that the present invention may be embodied in different waysand is not limited to the following embodiments. In the drawings,portions irrelevant to the description will be omitted for clarity. Likecomponents will be denoted by like reference numerals throughout thespecification.

Throughout the specification, when an element or layer is referred to asbeing “on”, “connected to”, or “coupled to” another element or layer, itmay be directly on, connected to, or coupled to the other element orlayer or intervening elements or layers may be present. In addition,unless stated otherwise, the term “includes” should be interpreted asnot excluding the presence of other components than those listed herein.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting. As used herein, thesingular forms, “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. Moreover,the terms “comprises”, “comprising”, “includes”, and/or “including” whenused in this specification, specify the presence of stated features,integers, steps, operations, elements, components, and/or groupsthereof, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings.

FIG. 1 is a perspective view of a metastructure having a zero elasticmodulus zone according to one embodiment of the present invention, andFIG. 2 is a front view of the metastructure of FIG. 1 .

Referring to FIG. 1 and FIG. 2 , a metastructure 100 having a zeroelastic modulus zone may include a first unit 110 and a second unit 130.

The first unit 110 may have a structure capable of buckling and may havea stress-strain relation having a zone corresponding to a negativeelastic modulus.

FIG. 3 shows a view illustrating deformation of the first unit of FIG. 1and a graph of the resulting stress-strain relation. In the followingdescription, reference will further be made to FIG. 3 .

Referring further to FIG. 3 , the first unit 110 may have a first upperframe 111, a first lower frame 112, and a first support frame 113.

The first upper frame 111 may extend horizontally.

The first lower frame 112 may extend horizontally and may be spacedapart from the first upper frame 111.

The first support frame 113 may be disposed between the first upperframe 111 and the first lower frame 112. The first support frame 113 maybe connected at an upper end thereof to the first upper frame 111 andmay be connected at a lower end thereof to the first lower frame 112.

The first support frame 113 may have any structure including one or morefirst support frames so long as the structure is able to buckle. In thisembodiment, the first support frame 113 may include a pair of firstsupport frames, the distance between which increases toward the firstlower frame 112.

As shown in FIG. 3(a), when a vertically downward compressive loadbegins to be applied to the first upper frame 111, the first supportframe 113 is deformed. During a certain period of time after applicationof the compressive load, for which the first support frame 113 isdeformed, a zone corresponding to a positive elastic modulus PEM appearsin the stress-strain relation, as shown in FIG. 3(c). Here, a positiveelastic modulus PEM indicates a positive slope of the stress-straincurve.

Then, when a critical buckling load CS is reached, buckling occurs inthe first support frame 113 (see FIG. 3(b)). From this point on, thefirst unit has a negative elastic modulus in a zone ranging from a firststrain E1, that is, a strain upon application of the critical bucklingload CS, to a second strain E2. That is, the stress-strain curve has anegative slope, such that stress in the first unit decreases despite acontinued increase in compressive load.

Beyond the zone corresponding to a negative elastic modulus NEM, thestress-strain curve may have a positive slope again if the first supportframe 113 continues to be compressed. That is, beyond the second strainE2, a zone corresponding to a positive elastic modulus may appear again.

In addition, the first unit 110 may further include a slit 114. The slit114 may be formed in the first support frame 113 and may extend in alongitudinal direction of the first support frame 113. The slit 114 maybe formed through the first support frame 113. The slit 114 in the firstsupport frame 113 can increase a length-to-cross-sectional area ratio ofthe first support frame 113, that is, slenderness of the first supportframe 113, thereby allowing buckling to occur more stably in the firstsupport frame 113.

The second unit 130 may be disposed adjacent to the first unit 110. Thesecond unit 130 may have a stress-strain relation having a zonecorresponding to a positive elastic modulus.

FIG. 4 shows a view illustrating deformation of the second unit of FIG.1 and a graph of the resulting stress-strain relation. In the followingdescription, reference will further be made to FIG. 4 .

Referring further to FIG. 4 , the second unit 130 may have a secondupper frame 131, a second lower frame 132, and a second support frame133.

The second upper frame 131 may be connected to the first upper frame 111and may extend horizontally. The first upper frame 111 and the secondupper frame 131 may be integrally formed with each other.

The second lower frame 132 may be connected to the first lower frame 112and may extend horizontally. The second lower frame 132 may be spacedapart from the second upper frame 131. The first lower frame 112 and thesecond lower frame 132 may be integrally formed with each other.

The second support frame 133 may be disposed between the second upperframe 131 and the second lower frame 132. The second support frame 133may be connected at an upper end thereof to the second upper frame 131and may be connected at a lower end thereof to the second lower frame132. The second support frame 133 may include a pair of second supportframes, the distance between which increases toward centers thereof.Upon application of compressive load, the second support frame 133 maybe deformed without buckling.

As shown in FIG. 4(a), when a vertically downward compressive loadbegins to be applied to the second upper frame 131, the second supportframe 133 is deformed. During application of the compressive load to thesecond support frame 133, the second support frame 133 is deformed, butdoes not buckle (see FIG. 4(b)). Accordingly, as shown in FIG. 4(c), thesecond unit may have a stress-strain relation having a zonecorresponding to a positive elastic modulus PEM.

Since the second unit 130 does not buckle, the second unit 130 has apositive elastic modulus in a zone ranging from a third strain E3, thatis, a strain at the start of deformation, to a fourth strain E4. Thatis, the stress-strain curve has a positive slope, such that stress inthe second unit increases as the compressive load increases.

FIG. 5 shows a view illustrating deformation of the metastructure havingthe zero elastic modulus zone of FIG. 1 and a graph of the resultingstress-strain relation.

Referring to FIG. 5(a) and FIG. 5(b), upon application of compressiveload to the metastructure 100 having the zero elastic modulus zone, anelastic modulus profile as shown in FIG. 5(c) may be produced throughsynthesis of a negative elastic modulus of the first unit 110 with apositive elastic modulus of the second unit 130. The metastructurehaving the synthesized elastic modulus profile may have a positiveelastic modulus PEM from an initial strain, that is, a strain at thestart of application of the compressive load, to a fifth strain E5, andmay have zero elastic modulus ZEM from the fifth strain E5 to a sixthstrain E6. Here, a zone ranging from the fifth strain E5 to the sixthstrain E6 may be predetermined as a target strain zone. That is, atarget strain zone, in which the metastructure can have zero elasticmodulus ZEM, may be predetermined through appropriate design of thenegative elastic modulus of the first unit 110 and the positive elasticmodulus of the second unit 130. The target strain zone may be varieddepending on devices to be transferred, the size thereof, adhesionpressure required for picking and placing the devices, and the like.

In the target strain zone, in which the metastructure has zero elasticmodulus ZEM, the metastructure may have zero stiffness. In other words,a stress level at the fifth strain E5, which is the starting point ofthe target strain zone, can remain constant in the target strain zone.

Upon application of an external compressive load to the metastructure100 having the zero elastic modulus zone, compressive stress generatedin the metastructure 100 increases to a certain level S until the fifthstrain E5 is reached. However, in the target strain zone ranging fromthe fifth strain E5 to the sixth strain E6, compressive stress in themetastructure 100 no longer increases and remains constant at the levelS.

This means that, when an appropriate external compressive load isapplied to the metastructure 100 having the zero elastic modulus zonesuch that the metastructure 100 is deformed only in the target strainzone, uniform adhesion pressure can be applied to devices to betransferred by the metastructure 100 having the zero elastic moduluszone.

Accordingly, even when there are factors making it difficult to applyuniform pressing force between an adhesive layer and micro-devices, suchas tolerances for a transfer apparatus, such as machining errors of aroller or a pressure plate and assembly tolerances, uneven heights ofthe micro-devices, warpage of a substrate, and the like, uniform contactpressure can be applied to different devices to be transferred byproviding an appropriate compressive load such that the metastructure100 having the zero elastic modulus zone is deformed in the targetstrain zone.

FIG. 6 is an exemplary view illustrating the relationship between strainand adhesion pressure in a conventional stamp, and FIG. 7 is anexemplary view illustrating the relationship between strain and adhesionpressure in the metastructure having the zero elastic modulus zone ofFIG. 1 .

First, in the case where multiple devices are picked from a substrateusing a conventional stamp, if the multiple devices have the sameheight, strains of the stamp deformed by pressure applied by respectivedevices are equal to one another, such that the same level of stress isgenerated in each deformed portion of the stamp and the same amount ofadhesion pressure is applied between the stamp and each of the devices.

However, if the height H2 of a second device 22 on the substrate 10 isgreater than the height H1 of a first device 20 on the substrate 10 (seeFIG. 6(a)), a strain B2 to which the stamp 30 is deformed by pressureapplied by the second device 22 is greater than a strain B1 to which thestamp 30 is deformed by pressure applied by the first device 20. Then,stress S2 in a portion of the stamp 30 pressed by the second device 22is greater than stress S1 in a portion of the stamp 30 pressed by thefirst device 20 (see FIG. 6(b)). Accordingly, the conventional stamp hasa positive elastic modulus PEM in a stress-strain relation thereof (seeFIG. 6(c)).

As a result, a large amount of force is locally applied to the seconddevice 22, causing damage to the second device 22. Even so, reducingpressing force of the stamp 30 applied to the second device 22 toprevent this problem can result in insufficient contact pressure betweenthe first device 20 and the stamp 30 or failure of the first device 20to be brought into contact with the stamp 30, making it impossible toprovide sufficient adhesion pressure to the first device 20.

Conversely, referring to FIG. 7 , the metastructure 100 having the zeroelastic modulus zone can allow stress S1 in a portion of themetastructure 100 pressed by the first device 20 to be equal to stressS2 in a portion of the metastructure 100 pressed by the second device 22even when the height H2 of the second device 22 on the substrate 10 isgreater than the height H1 of the first device 20 on the substrate 10and thus a strain B2 of the metastructure 100 deformed by pressureapplied by the second device 22 is greater than a strain B1 of themetastructure 100 deformed by pressure applied by the first device 20.That is, the metastructure 100 may have zero elastic modulus ZEM in aspecific zone of the stress-strain relation. Accordingly, uniformadhesion pressure can be applied between the metastructure 100 havingthe zero elastic modulus zone and the different devices 20, 22.

The first unit 110 and the second unit 130 may be formed of the samematerial. The first unit 110 and the second unit 130 may be formed of apolymer, rubber, or the like.

FIG. 8 is an exemplary diagram illustrating an example of parallelarrangement of metastructures each having a zero elastic modulus zone asshown in FIG. 1 .

Referring to FIG. 8 , multiple metastructures 100 each having a zeroelastic modulus zone may be arranged in parallel on a virtual plane.Here, the first unit 110 and the second unit 130 may be alternatelyarranged to be adjacent to each other. In this way, through arrangementof the multiple metastructures in a plane, the metastructure 100 havingthe zero elastic modulus zone according to the present invention can bescaled up in area, and can be fabricated in the form of a film roll orsheet roll.

Next, a method for designing a metastructure having a zero elasticmodulus zone will be described.

FIG. 9 is a flowchart of a method for designing a metastructure having azero elastic modulus zone according to one embodiment of the presentinvention.

The method may include a first unit formation step S210, a second unitformation step S220, and a compensation step S230.

In the first unit formation step S210, a first unit is formed, whereinthe first unit has a structure capable of buckling and has astress-strain relation having a zone corresponding to a negative elasticmodulus.

In the second unit formation step S220, a second unit is formed, whereinthe second unit is disposed adjacent to the first unit and has astress-strain relation having a zone corresponding to a positive elasticmodulus.

In the compensation step S230, synthesis of the negative elastic modulusof the first unit with the positive elastic modulus of the second unitis performed such that the metastructure has zero elastic modulus in apredetermined target strain zone.

In the compensation step S230, if an elastic modulus profile obtainedthrough synthesis of the negative elastic modulus of the first unit withthe positive elastic modulus of the second unit has a slope of greaterthan zero in the target strain zone, the slope of the elastic modulusprofile is compensated to zero by adjusting the elastic modulus of thefirst unit or the second unit or by adjusting the shape of the firstunit or the second unit.

FIG. 10 is an exemplary view illustrating an example of shape adjustmentof the first unit of FIG. 1 , FIG. 11 is an exemplary view illustratingan example of shape adjustment of the second unit of FIG. 1 , and FIG.12 is a graph describing the compensation step of FIG. 9 .

First, when a first unit 110, the width and height of which have thesame basic dimension L, is defined as a basic first unit, as shown inFIG. 10(a), the size and shape of the first unit 110 may be adjusted, asshown in FIG. 10(b) to FIG. 10(e).

Referring to FIG. 10(b), the basic first unit may be modified into afirst unit 110 a by increasing both the width and height thereof by ktimes the basic dimension L. Here, the lengths of a first upper frame111 a, a first lower frame 112 a, and a first support frame 113 a may begreater than the lengths of a first upper frame 111, a first lower frame112, and a first support frame 113 of the basic first unit 110,respectively.

Alternatively, referring to FIG. 10(c), the basic first unit may bemodified into a first unit 110 b by increasing the width thereof by ntimes with the height thereof fixed to the basic dimension L. Here, thelength of a first support frame 113 b may be equal to the length of thefirst support frame 113 of the basic first unit 110, and the lengths ofthe first upper frame 111 b and the first lower frame 112 b may be ntimes the lengths of the first upper frame 111 and the first lower frame112 of the basic first unit 110, respectively.

Alternatively, referring to FIG. 11(d), the basic first unit may bemodified into a first unit 110 c by increasing the height thereof by mtimes with the width thereof fixed to the basic dimension L. Here, thelengths of a first upper frame 111 c, a first lower frame 112 c, and afirst support frame 113 c may be equal to the lengths of the first upperframe 111, the first lower frame 112, and the first support frame 113 ofthe basic first unit 110, respectively, and the thicknesses of the firstupper frame 111 c and the first lower frame 112 c may be greater thanthe thicknesses of the first upper frame 111 and the lower frame 112 ofthe first basic unit 110, respectively.

Alternatively, referring to FIG. 10(e), the basic first unit may bemodified into a first unit 110 d by increasing the width thereof by ntimes and increasing the length thereof by m times. Here, the length ofa first support frame 113 d may be equal to the length of the firstsupport frame 113 of the first basic unit 110, the lengths of a firstupper frame 111 d and a first lower frame 112 d may ben times thelengths of the first upper frame 111 and the first lower frame 112 ofthe basic first unit 110, respectively, and the thicknesses of the firstupper frame 111 d and the first lower frame 112 d may be greater thanthe thicknesses of the first upper frame 111 and the first lower frame112 of the basic first unit 110, respectively.

And, when a second unit 130, the width and height of which have the samebasic dimension L, is defined as a basic second unit, as shown in FIG.11(a), the size and shape of the second unit 130 may be adjusted, asshown in FIG. 11(b) to FIG. 11(e).

Referring to FIG. 11(b), the basic second unit may be modified into asecond unit 130 a by increasing both the width and height thereof by ktimes. Here, the lengths of a second upper frame 131 a, a second lowerframe 132 a, and a second support frame 133 a may be greater than thelengths of a second upper frame 131, a second lower frame 132, and asecond support frame 133 of the basic second unit 130, respectively.

Alternatively, referring to FIG. 11(c), the basic second unit may bemodified into a second unit 130 b by increasing the width thereof by ntimes with the height thereof fixed to the basic dimension L. Here, thelength of a second support frame 133 b may be equal to the length of thesecond support frame 133 of the second basic unit 130, and the lengthsof a second upper frame 131 b and a second lower frame 132 b may be ntimes the lengths of the second upper frame 131 and the second lowerframe 132 of the basic second unit 130, respectively.

Alternatively, referring to FIG. 11(d), the basic second unit may bemodified into a second unit 130 c by increasing the height thereof by mtimes with the width thereof fixed to the basic dimension L. Here, thelengths of a second upper frame 131 c, a second lower frame 132 c, and asecond support frame 133 c may be equal to the lengths of the secondupper frame 131, the second lower frame 132, and the second supportframe 133 of the basic second unit 130, respectively, and thethicknesses of the second upper frame 131 c and the second lower frame132 c may be greater than the thicknesses of the second upper frame 131and the second lower frame 132 of the basic second unit 130,respectively.

Alternatively, referring to FIG. 11(e), the basic second unit may bemodified into a second unit 130 d by increasing the width thereof by ntimes and increasing the height thereof by m times. Here, the length ofa second support frame 133 d may be equal to the length of the secondsupport frame 133 of the basic second unit 130, the lengths of a secondupper frame 131 d and a second lower frame 132 d may ben times thelengths of the second upper frame 131 and the second lower frame 132 ofthe basic second unit 130, respectively, and the thicknesses of thesecond upper frame 131 d and the second lower frame 132 d may be greaterthan the thicknesses of the second upper frame 131 and the second lowerframe 132 of the basic second unit 130, respectively.

When an elastic modulus profile obtained through synthesis of thenegative elastic modulus of the first unit with the positive elasticmodulus of the second unit has a slope greater than zero in the targetstrain zone ranging from a first strain E1 to a second strain E2, asshown in FIG. 12(a), that is, when the metastructure has a positiveelastic modulus PEM in the target strain zone, in the compensation stepS230, an adjustment may be made to increase the absolute value of thenegative elastic modulus of the first unit or to reduce the absolutevalue of the positive elastic modulus of the second unit.

Alternatively, when the elastic modulus profile obtained throughsynthesis of the negative elastic modulus of the first unit with thepositive elastic modulus of the second unit has a slope greater thanzero in the target strain zone ranging from the first strain E1 to thesecond strain E2, in the compensation step S230, an adjustment may bemade to reduce the lengths of the first upper frame and the first lowerframe or to increase the lengths of the second upper frame and thesecond lower frame.

Alternatively, when the elastic modulus profile obtained throughsynthesis of the negative elastic modulus of the first unit with thepositive elastic modulus of the second unit has a slope greater thanzero in the target strain zone ranging from the first strain E1 to thesecond strain E2, in the compensation step S230, an adjustment may bemade to increase the thicknesses of the first upper frame and the firstlower frame or to reduce the thicknesses of the second upper frame andthe second lower frame. In this way, the synthesized elastic modulusprofile can have a slope of zero. That is, the metastructure can havezero elastic modulus in the target strain zone.

When the elastic modulus profile obtained through synthesis of thenegative elastic modulus of the first unit with the positive elasticmodulus of the second unit has a slope smaller than zero in the targetstrain zone ranging from the first strain E1 to the second strain E2, asshown in FIG. 12(b), that is, when the metastructure has a negativeelastic modulus NEM in the target strain zone, in the compensation stepS230, an adjustment may be made to reduce the absolute value of thenegative elastic modulus of the first unit or to increase the absolutevalue of the positive elastic modulus of the second unit. Alternatively,an adjustment may be made to increase the lengths of the first upperframe and the first lower frame or to reduce the lengths of the secondupper frame and the second lower frame. Alternatively, an adjustment maybe made to reduce the thicknesses of the first upper frame and the firstlower frame or to increase the thicknesses of the second upper frame andthe second lower frame. In this way, the synthesized elastic modulusprofile can have a slope of zero. That is, the metastructure can havezero elastic modulus in the target strain zone.

FIG. 13 shows an exemplary view of a serial array of metastructures eachhaving a zero elastic modulus zone as shown in FIG. 1 and a graph of theresulting stress-strain relation. In FIG. 13(a), a simplified shape ofthe metastructure is shown.

Referring to FIG. 13 , multiple metastructures 100 each having a zeroelastic modulus zone may be vertically arranged in series. That is, themultiple metastructures 100 may be stacked in multiple layers along theaxis of load application. In the serial array, the first unit 110 andthe second unit 130 may be arranged in any suitable relationship withrespect to each other. In the serial array, the size and shape of themetastructure 100 may be varied from layer to layer. Then, the amount ofdisplacement of the metastructure 100 may be different from layer tolayer although the amount of load applied to the metastructure 100 isthe same for every layer. In this way, the serial array of themetastructures can have zero elastic modulus ZEM1/ZEM2, that is, canexperience constant stress S1/S2, in multiple strain zones, that is, astrain zone ranging from a first strain E1 to a second strain E2 and astrain zone ranging from a third strain E3 to a fourth strain E4.

Although the metastructure has been described as being a transfer filmused for device transfer for convenience, the metastructure may be usedin various applications requiring uniformity in load distribution,including a mattress or cushion for preventing bedsores occurring inbedridden patients, a control unit for passive load control or passivepressure control, and the like.

Although some embodiments have been described herein, it should beunderstood that these embodiments are provided for illustration only andare not to be construed in any way as limiting the present invention,and that various modifications, changes, alterations, and equivalentembodiments can be made by those skilled in the art without departingfrom the spirit and scope of the invention. For example, componentsdescribed as implemented separately may also be implemented in combinedform, and vice versa.

The scope of the present invention is indicated by the following claimsand all changes or modifications derived from the meaning and scope ofthe claims and equivalents thereto should be construed as being withinthe scope of the present invention.

1. A metastructure having a zero elastic modulus zone, the metastructurecomprising: a first unit having a structure capable of buckling andhaving a stress-strain relation having a zone corresponding to anegative elastic modulus; and a second unit disposed adjacent to thefirst unit and having a stress-strain relation having a zonecorresponding to a positive elastic modulus, the metastructure havingzero elastic modulus in a predetermined target strain zone throughsynthesis of the negative elastic modulus of the first unit with thepositive elastic modulus of the second unit.
 2. The metastructureaccording to claim 1, wherein the first unit comprises: a first upperframe extending horizontally; a first lower frame extending horizontallyand spaced apart from the first upper frame; and a pair of first supportframes each connected at an upper end thereof to the first upper frameand connected at a lower end thereof to the first lower frame, adistance between the pair of first support frames increasing toward thefirst lower frame such that the pair of first support frames bucklesupon application of compressive load.
 3. The metastructure according toclaim 2, wherein the first unit further comprises: a slit formed throughthe first support frame and extending in a longitudinal direction of thefirst support frame.
 4. The metastructure according to claim 2, whereinthe second unit comprises: a second upper frame connected to the firstupper frame and extending horizontally; a second lower frame connectedto the first lower frame and extending horizontally; and a pair ofsecond support frames each connected at an upper end thereof to thesecond upper frame and connected at a lower end thereof to the secondlower frame, a distance between the pair of second support framesincreasing toward centers thereof such that the pair of second supportframes is deformed without buckling upon application of compressiveload.
 5. The metastructure according to claim 4, wherein the first upperframe is integrally formed with the second upper frame and the firstlower frame is integrally formed with the second lower frame.
 6. Themetastructure according to claim 1, wherein the first unit and thesecond unit are formed of the same material.
 7. The metastructureaccording to claim 1, wherein the metastructure comprises multiplemetastructures arranged on a virtual plane, and the first unit and thesecond unit are alternately arranged to be adjacent to each other. 8.The metastructure according to claim 7, wherein the first unit and thesecond unit are stacked in multiple layers.
 9. A method for designing ametastructure having a zero elastic modulus zone, comprising: a firstunit formation step in which a first unit is formed, the first unithaving a structure capable of buckling and having a stress-strainrelation having a zone corresponding to a negative elastic modulus; asecond unit formation step in which a second unit is formed, the secondunit being disposed adjacent to the first unit and having astress-strain relation having a zone corresponding to a positive elasticmodulus; and a compensation step in which the negative elastic modulusof the first unit is synthesized with the positive elastic modulus ofthe second unit such that the metastructure has zero elastic modulus ina predetermined target strain zone.
 10. The method according to claim 9,wherein, in the compensation step, when an elastic modulus profileobtained through synthesis of the negative elastic modulus of the firstunit with the positive elastic modulus of the second unit has a slopegreater than zero in the target strain zone, an adjustment is made toincrease an absolute value of the negative elastic modulus of the firstunit or to reduce an absolute value of the positive elastic modulus ofthe second unit.
 11. The method according to claim 9, wherein: the firstunit comprises first upper and lower frames each extending horizontallyand vertically spaced apart from each other and a first support frameconnected at an upper end thereof to the first upper frame and connectedat a lower end thereof to the first lower frame, the first support framebuckling upon application of compressive load; the second unit comprisesa second upper frame connected to the first upper frame and extendinghorizontally, a second lower frame connected to the first lower frameand extending horizontally, and a second support frame connected at anupper end thereof to the second upper frame and connected at a lower endthereof to the second lower frame, the second support frame beingdeformed without buckling upon application of compressive load; and, inthe compensation step, when an elastic modulus profile obtained throughsynthesis of the negative elastic modulus of the first unit with thepositive elastic modulus of the second unit has a slope greater thanzero in the target strain zone, an adjustment is made to reduce lengthsof the first upper frame and the first lower frame or to increaselengths of the second upper frame and the second lower frame.
 12. Themethod according to claim 9, wherein: the first unit comprises firstupper and lower frames each extending horizontally and vertically spacedapart from each other and a first support frame connected at an upperend thereof to the first upper frame and connected at a lower endthereof to the first lower frame, the first support frame buckling uponapplication of compressive load; the second unit comprises a secondupper frame connected to the first upper frame and extendinghorizontally, a second lower frame connected to the first lower frameand extending horizontally, and a second support frame connected at anupper end thereof to the second upper frame and connected at a lower endthereof to the second lower frame, the second support frame beingdeformed without buckling upon application of compressive load; and, inthe compensation step, when an elastic modulus profile obtained throughsynthesis of the negative elastic modulus of the first unit with thepositive elastic modulus of the second unit has a slope greater thanzero in the target strain zone, an adjustment is made to increasethicknesses of the first upper frame and the first lower frame or toreduce thicknesses of the second upper frame and the second lower frame.